refactor(playlists): scope module state in PlaylistsProvider

Lift the Playlists module's shared local state (rail name filter + selected
playlist) out of App into a split-context PlaylistsProvider, mirroring
FeedFiltersProvider. Header, PlaylistsRail, and the Playlists detail pane read
it via usePlaylists()/usePlaylistsActions() instead of props drilled through
App; the modules take only a uniform `me` prop now. App loses two useStates and
the selected-playlist persistence helper. (Platform S6b.2)

frontend/src/App.tsx

@@ -134,7 +134,6 @@ export default function App() {
   // Client-side name filters for the Channels + Playlists lists — lifted here so the shared top
   // SearchBar can drive them (the modules read/seed them via props).
   const [channelsSearch, setChannelsSearch] = useState("");
-  const [playlistsSearch, setPlaylistsSearch] = useState("");
   const [wizardOpen, setWizardOpen] = useState(false);
   // Channel status chip, persisted so a reload (F5) keeps it; clamp a stale value at render.
   const [channelFilterRaw, setChannelFilter] = useAccountPersistedState(LS.channelFilter, "all");
@@ -246,17 +245,6 @@ export default function App() {
     writeAccount(LS.playlistsCollapsed, next);
     api.savePrefs({ playlistsCollapsed: next }).catch(() => {});
   }
-  // The selected playlist — App state so the App-level PlaylistsRail and the module's detail pane
-  // (Playlists) stay in sync. Persisted so a reload keeps it (it's not in the URL).
-  const [selectedPlaylistId, setSelectedPlaylistIdState] = useState<number | null>(() => {
-    const s = getAccountRaw(LS.playlist);
-    return s ? Number(s) : null;
-  });
-  const setSelectedPlaylistId = (id: number | null) => {
-    setSelectedPlaylistIdState(id);
-    if (id != null) setAccountRaw(LS.playlist, String(id));
-  };
-
   useEffect(() => applyTheme(theme), [theme]);
 
   // Apply the draft prefs locally for instant preview (their localStorage mirrors update via
@@ -611,10 +599,7 @@ export default function App() {
       )}
       {page === "playlists" && !channelView && (
         <PlaylistsRail
-          canWrite={meQuery.data!.can_write}
-          search={playlistsSearch}
-          selectedId={selectedPlaylistId}
-          setSelectedId={setSelectedPlaylistId}
+          me={meQuery.data!}
           layout={panelLayouts.playlists}
           setLayout={(l) => setPanelLayout("playlists", l)}
           collapsed={playlistsCollapsed}
@@ -663,8 +648,6 @@ export default function App() {
                 setPlexQ={setPlexQ}
                 channelsSearch={channelsSearch}
                 setChannelsSearch={setChannelsSearch}
-                playlistsSearch={playlistsSearch}
-                setPlaylistsSearch={setPlaylistsSearch}
                 onYtSearch={enterYtSearch}
                 onGoToFullHistory={() => {
                   setChannelFilter("needs_full");
@@ -715,11 +698,7 @@ export default function App() {
           ) : page === "audit" && meQuery.data!.role === "admin" ? (
             <AuditLog />
           ) : page === "playlists" ? (
-            <Playlists
-              canWrite={meQuery.data!.can_write}
-              selectedId={selectedPlaylistId}
-              setSelectedId={setSelectedPlaylistId}
-            />
+            <Playlists me={meQuery.data!} />
           ) : page === "notifications" ? (
             <NotificationsPanel onFocusChannel={focusChannel} />
           ) : page === "messages" && !meQuery.data!.is_demo ? (